text:
What is the difference between a fix, a waypoint and an intersection?
It seems these terms are used interchangeably. Are they the same thing? Do they all refer to the points in space that are given 5-letter names?

My contribution: those shown as triangles on low altitude IFR or sectional charts are "fixes" and those shown as 4 point stars are "waypoints". If the symbol is filled, it is a compulsory reporting point. If not filled, it is a non-compulsory reporting point. Crossed arrows on airways are "intersections"

No, they are not interchangeable and indeed, have well defined meanings.
A fix is an arbitrary point in space used to establish current position calculated by referring to external references.  You take a fix to determine where you are now.  A fix might be permanent, for example a compulsory reporting point, or it might be determined by the pilot in advance in order to fly a non-airways route (e.g. when flying VFR) and then checked along the way using dead reckoning and reference to external systems or features to check that the plan is being flown accurately.  It might also be requested by ATC, e.g. "report when overhead the railroad yard" or calculated to establish where you are, e.g. taking a fix from an astrolabe on a night oceanic crossing.

From FlightGear.
A waypoint is fixed point in 2D space (latitude and longitude) used to define points along a route.  They are named, and are referenced in a plan.  You fly from one waypoint to the next, along a route.  A waypoint is where you are flying to.  It is normally positioned where there is a change of course or altitude.
These are the navigation positions given the 5 letter names you ask about.

From SailTrain.

An intersection is where two airways cross. Here, the Victor airways 15 and 76 cross at the intersection.  In this particular case, the chart symbol further shows that the V76 airway does not use the intersection, in which case the chart will include a note of the intersection usage.

From Jepptech.
Now sorry about this, but having said they are not interchangeable, it's not that simple.  A waypoint is also a fix (a fix is any 2D point).  But you do not call a waypoint a fix.  A fix is a 2D point which is not a waypoint, but is used for navigation.  A fix might be also be a lat and long defining the beginning of an arrival or departure procedure where you leave or enter an airway.
An intersection is also a fix, but it only exists to define where two airways cross (or where any other 2 lines cross, e.g. the 170 degree and 046 degree radial from two NDB beacons) so is called an intersection, not a fix.
In that sense, they are all fixes but the name has meaning.

a "fix" could also be an "holding fix" and in that case would have a slight different meaning, wouldn't it?

@Federico I'm not sure if it is.  The holding pattern is anchored on a "fix", but it's still a fix.  You might also be instructed to hold at a waypoint.

So what are the points in space with the 5-letter names, like BRBBQ or FNCHR or LOONR?

@TomMcW Just edited at the same time as your comment to explain exactly that!  They are waypoints.

When you say V76 "does not use the intersection," what does V15 use it for?

@TomMcW Even though the intersection defines where 2 airways cross, it has no purpose on V76.  On V15, you might be asked to report when crossing the intersection, or to hold to the North of it until cleared.  No such instruction would be issued if flying along V76.

Must be difficult to calculate a fix from those red spots when the lines to them are so wavy... Is that because of turbulence?  :D

i don't think this is right @Simon, because it doesn't explain why we have both Missed Approach Fix (MAP) and MIssed Approach Point (MAP). I just researched this for OP's follow-up question http://aviation.stackexchange.com/questions/27305/what-is-the-difference-between-fixes-and-waypoints-on-an-approach-plate

ugh -- MAF and MAP

A fix is a point used to check longitudinal position along a linear course, in formal use a fix is determined by intercepting specific ground based navaids. Named fixes are those marked on charts and are included in FSS and ATC databases. Named fixs improve communication and if used for changing route segments they have been checked for signal strength and altitude requirements. The fix can either be the interception of an off airway nav signal, the use of DME, or the intersection of two airways.(such as VOR/VOR radials, DME/DME, VOR/DME, NDB/VOR) A fix can also be a "facility" which is the actual navaid installation. eg the point of station passage when directly over a VOR. The key bit that makes a fix a fix and not just another point along the way is that position between fixes is only an estimate while the fix is a point with a positive signal change, like breaking a ribbon at a finish line rather than just estimating 100 yards have passed. This goes back to non-radar ATC where they spaced aircraft based on estimated speed and time with an E6B and they could only be certain of the aircraft position when the aircraft reported positive crossing known navigation elments. Even older inertial RNAV required occasional fixes to re-calibrate periodically. (similar to holding straight and level for a moment to check the heading indicator against the compass) Similarly, fixes are needed for determining with certainty the latest start of climb that will ensure obstacle clearance at a minimum gradient. Important to the concept is that the course is not defined by the navaid that is providing the fix; one provides longitudinal position and the other provides lateral position and both positions are relative to the location of a local facility that is attached to the ground. Because of this last bit [with sufficient altitude] you could fly along a traditional airway route without determining any enroute fixes.
An intersection is where two airways join or cross, most of these are also used as a named fix [or waypoint depending on the type of airway]. Although there are a few airway crossings without a name, likely because they have not been evaluated or flight checked for turning radius obstacle clearance or minimum crossing altitudes. (These would only be used for changing airways at the discretion and calculations of the pilot, and possibly would not be approved as part of an instrument flight plan. Though I have not tried to file with such an intersection so this is speculation.)
A waypoint is determined the same as any other GPSS point along your way, unlike a fix there is no positive signal change or other physical property unique to that location, rather it is just another calculated point, generally defined in terms of latitude and longitude. Unlike fixes these calculated points are nessessary to define both the route and position along the route.
Waypoints can be defined adhoc by the user or named and published. Published waypoints have additional metadata, they may be flyby or flyover, and have a certain associated navspec so the nav computer can set the correct course deviation sensitivity based on the phase of flight: enroute, terminal area, final approach, or oceanic. (full scale deflection of 2nm, 1nm, 0.3nm, and 10nm respectively. But know this is basic view, full navspec is more complex, because bureaucrats.) With GPSS the nav computer calculated a precise position continuously along the way so there isn't such a need for fixing important locations, for example the gradient and start point of a climb can be accurately calculated anywhere along the route rather than being a fixed point for all aircraft. So waypoints are more for defining a route, and published named waypoints are a convenient radio shorthand(rather than listing full latitude and longitude) and pre-arranged backup for managing traffic in the case of lost radar or radio.
The criteria for setting accuracy tolerances is also quite different. Often a fix tolerance is given in angles(so fixes far from a navaid will have a wide tolerance) while a waypoint tolerance will be a radius around the point calculated from a given navspec.(categories of RNAV equipment sensitivity and reliability) With DME fixes, slant range causes the fix to shift laterally as an aircraft descends or climbs(ie in a hold over a fix) but a waypoint does not shift.

The definition of fix above by Simon is "close" but not perfect. The definition appears to be implying that the fix just for "own ship", that is, my present position. The fix IS an arbitrary point in space. The definition should stop there. A fix MAY be used if needed to help establish your current position or may even be the estimate of your current position. You may want to get a fix on some other entity such as a coastline feature or another aircraft or vessel. For example, one generates a RADAR fix on an aircraft by knowing the location of the RADAR antenna, the azimuth angle the RADAR was pointing when "painting" the aircraft/target, and the duration of time for the RADAR signal to travel to and return from a reflecting aircraft. Thus a "fix" may have nothing to do with establishing one's current position.

I don’t understand your logic.  The last line seems to contradict the rest of your answer.


text:
Can one ARTCC take over for another ARTCC in an emergency?
Earlier today the ZNY ARTCC was shut down due to COVID-19. This resulted in a temporary ground stop for incoming flights while a contingency plan was being activated. When certain sectors within an ARTCC are shut down, as happened yesterday at ZID aircraft are routed aground the sectors, but it would be very difficult to route around an entire ARTCC facility’s airspace. In fact, as ZNY was shut down, aside from the temporary ground stop, flights over the ZNY airspace appeared to continue as normal.
I make the assumption that the centers are connected and that when one center has to shut down entirely for some reason that the other ARTCC’s are capable of taking over for them and providing the same radar service. How true is this assumption?

Note: There are conflicting reports at this time as to whether the entire ARTCC had to shut down or just some sectors. The question still stands as to what would happen if an entire center had to close.

ZAU was shutdown completely in 2014.   It caused a lot of difficulty as the space was divided among multiple other centers with less-than-perfect radar coverage.

How would they see the radar?  Is it like Star Trek where they can just wave their hand and kick their radar over to another control center?  I was under the impression that FAA ATC gear is all 1950s aesthetic, and looks like you'd expect railroad CTC gear to look.

Generally speaking, no.
As for the specific situation, New York Oceanic has been closed since midnight UTC:

DUE TO AN OPERATIONAL EMERGENCY NEW YORK AIR ROUTE TRAFFIC CONTROL CENTER IS DISCONTINUING AIR TRAFFIC SERVICES IN THE NEW YORK OCEANIC FIR UNTIL FURTHER NOTICE.FLIGHTS CHOOSING TO ENTER NEW YORK CENTER AIRSPACE SHOULD EXPECT ONLY ADVISORY SERVICE.
  NOTAM A0249/20 refers.

Most ATS units have contingency procedures in place to dictate what happens if the unit needs to close on short notice, for example during an evacuation. It is quite common to have agreements with adjacent units to help clear the airspace ("clear-the-sky" systems). This is possible if adjacent units have RADAR and radio coverage that overlaps with that of the unit being evacuated. While not able to provide regular service, adjacent units can monitor traffic and make sure everyone gets out of the evacuated airspace safely, after which that piece of airspace is closed.
In order for an adjacent ATS unit to actually take over and provide normal service, several things would be required:

Additional staffing. It might not be possible to just call more people to work, as that would mess up the entire roster in days and weeks to come, seriously affecting the non-evacuated unit.
Additional working positions for the extra staff to actually sit and work, while still maintaining a number of backup positions in case of equipment failure.
Staff must have knowledge of local rules and procedures of the airspace they are taking over, and have valid and current ratings to be allowed to control it. You can't keep your rating current if you don't use it regularily. Just like you can't just take an Airbus-pilot and ask them to fly a Boeing-aircraft because the Boeing crew called in sick.
RADAR coverage must be sufficient. This could be achieved by sharing RADAR-data between facilities, but if one ATS unit needs to evacute, their technicians have probably evacuated too - which means the data cannot be used since there is no one to monitor the status of technical equipment.
Radio coverage must be sufficient (see above)
All telephone lines must be re-routed (which is doable, if the system is set up for it)

What is more likely to happen is that the unit evacuating will move into a contingency facility from where they are able to provide anything from a very limited to full service. Some airports have old control towers that are still being maintained as contingency positions, and area centres might have dedicated backup facilities, or possibly training facilities (simulator positions) that can be switched over to a live environment. Of course, if all the staff that happened to be on shift at the time of evacuation needs to be quarantined due to a contagious disease, you will have a pretty big staffing issue.

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text:
What is METAR and how is it read?
I was reading an article about TAM Airlines Flight 3054 crash and I saw the following:
METAR

SBSP 172200z 35008kt 7000 -ra Bkn008 Ovc070 15/14 Q1018
SBSP 172200z 35008kt 7000 -ra Bkn008 Ovc070 15/14 Q1018
SBSP 172100z 34008kt 6000 -ra Bkn009 Ovc070 16/14 Q1018
SBSP 172030z 32009kt 7000 -ra Bkn013 Ovc080 16/14 Q1018
SBSP 172000z 31012kt 8000 -ra Bkn016 Ovc080 17/14 Q1018
SBSP 171900z 34009kt 9999 -ra Bkn016 Bkn080 18/15 Q1017

Questions:

What is METAR?
How is it read?
What is the difference between the International METAR codes and the
North American METAR codes?

There is a lot of info on the internet on how to read METARS.

What has always bothered me is why they continue to be published in the most cryptic format on the planet well into the 21st century.

@romkyns - what you see as "cryptic", others see as "terse", after a little practice they can quickly get the information they need from 55 characters of text. Making the text more verbose wouldn't necessarily make it more usable to those that use it regularly.

@romkyns What alternative scheme would you suggest to the one which is standardised, usable by people who do not speak English, can convey large amounts of information in a short line of characters, is unambiguous, can be read by software and above all, is simple for people who use them to understand?  Seems to tick the boxes.

@Simon - Sure, but most of those boxes have nothing to do with publishing for human consumption. There is a reason why we don't show web pages as raw HTML after all, and raw HTML checks all those boxes, too.

Guys, I don't know if it's a dumb question, but I what is the difference between METAR and ATIS?

METAR is a Meteorological Aerodrome Report which is for a specific place, at a specific time.
The first line is a report from Sao Paulo at 22:00 on the 17th.
You can use a service such as this one to decode METAR reports.
The rest of the lines are more reports for different time and days.
The groups are:
 SBSP       Reporting station ICAO code
 172220Z    Day of the month (17) and current time in UTC (2220) (Z for Zulu time)
 35008KT    Wind from 350 degrees true at 8 knots
 7000       Horizontal visibility on the ground in metres
 -RA        Current weather (RA = rain), the minus indicates light, plus indicates heavy
 BKN008     Broken clouds at 800 feet
 OVC070     Overcast clouds at 7000 feet
 15/14      Temperature 15C, dew-point 14C
 Q1018      regional atmospheric pressure 1018hPa / US systems use inHG / others use millibars

Note that the linked decoder wants all the letters in the report to be upper case. With the mixed-case strings from the Avherald article, it misses some of the parts of the report and decodes it to, say, "ceiling unlimited".

@HenningMakholm  Thanks.  For other readers, there are multiple decoders on the web and apps for all the usual smart phone platforms.

About 15 years ago, I wrote a METAR decoder, and found that there were a number of stations that sent invalid encoding that would've gone unnoticed by someone trained to read it.  I want to say that one case was 'OK' and '0K' being swapped.  (maybe in 'CAVOK'.  A few were out of order (eg, cloud cover before weather)

One interesting quirk of METAR is that temperatures below zero are represented with an M, e.g. M02 for -2°C.

@hobbs Unless it's in the remarks section, where they use 0 and 1 for the sign. :)

Is there any place with the official METAR decoding?

According to AC 00-45G a METAR stands for "Aviation Routine Weather Report." It seems the METAR acronym is a throw back to the old days before the METAR covered international regulations.

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text:
What should a pilot do to perform a successful emergency water landing?

What should a pilot do to perform a successful emergency water landing, also known as ditching of a big commercial jet?
Is there any checklist, or best practices, like "elevate the nose" or "retract the landing gear", to make it safer?
Are commercial Jets buoyant?

ditching http://www.flightglobal.com/blogs/wp-content/uploads/mt/flightglobalweb/blogs//learmount/Ditching.jpg

As I mentioned in the related question, there is a ditching checklist and the plane is certified for ditching. That report mentioned that reaching the required conditions were extremely difficult with no engine power, so that suggests it is fairly difficult. Also, that plane clearly floated.

Commercial aircraft will float for at least long enough for everyone to get out (90 seconds) and onto the emergency slides/rafts,

What should a pilot do?

Follow the checklist?

Is there any checklist?

There are many such checklists in the intertubes and whole books have been written on the subject
Here's the start of one for 737s

For comparison, here's one for a Cessna light aircraft

Are commercial jets buoyant?

Yes, initially, if substantially in once piece. We know that because several intrepid pilots have tested this idea (obligatory hat-tip to Sullenberger).
It makes sense that the fuel tanks in the wings, especially once emptied of fuel, are buoyant. The wings are obviously capable of supporting the fuselage. The fuselage is a pressurised tube and should be buoyant too, until the passengers and crew start making large holes in it.

what's the next page say, "pray to your favourite deity"?

@RedGrittyBrick:  Remember full fuel tanks are also bouyant!  Avgas and Jet-A float on water.  For sure, the full fuel tank is not as bouyant as an empty one...  but fuel floats!

@SkipMiller: Good point (though I guess it's the average density including metal skin and other parts that counts). I've inserted some words to suggest what you said.

@RedGrittyBrick Gotcha. I didn't mean that it negatively affected your answer. It illustrated your point and was a valid example of the existence of checklist procedures for ditching. As I pilot I just didn't like that particular checklist myself :)

One to add to your own checklists - partially open the doors before touching down, and open the ASAP after landing... the differential pressure can be an absolute bitch to overcome once water is pressing on the outside of the doors

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text:
Where is the regular wheel brake input on modern airliners?
I learned that on modern airliners, the Rudder input is given by the pedals located under the pilot's feet, and that got me thinking:

how do the pilots give the command to brake the plane in order to slow it down on ground (landing/taxing)?
Is the parking brake and "regular" wheel brake part of the same system?

related: What is differential braking? and What is the advantage of combining the rudder and brake pedals in aircraft?

The same way it is done in small airplanes and older airlines -- toe brakes.
The rudder pedals translate forward and back to actuate the rudder and they pivot around the lateral axis to actuate the brake system.  Each pedal independently controls only the brakes on its side of the airplane (e.g both pilots left toe brake actuates the brakes on the left main gear).
Planes will often have an emergency or parking brake, which will be a lever somewhere that actuates the brake system.  This system, outside of emergencies is only used when the plane is not moving and you want it to remain that way.
Larger airplanes with also sometimes have autobrakes which provide a triggered automatic application of a certain level of braking.  This kind of system is used both to provide automatic maximum braking for a rejected takeoff (RTO) and some lesser automatic braking upon landing rollout.
To summarize, for taxi and ground movement the brake input is coming from the toe brakes.  When the aircraft is stopped, brake input will be transferred from the toe brakes to the parking brake.  When the plane lands, if it is so equipped and enabled, the autobrakes will begin brake application and the pilot will take over with the toe brakes and continue to use toe brakes for the taxi in.

The brake controls are located in the rudder pedals themselves. The manual braking is achieved by pressing the top part of the rudder pedals (so called toe-brakes). See this video:

Differential braking is achieved by pressing the rudder pedals on one side.
The parking and 'regular' wheel brakes are usually part of the same system.


text:
What should I do if I get a fuel vent blockage in flight?
I'm flying C172s, and I have a question. During flight if a fuel vent (located on the left side) becomes blocked due to a bird strike or icing what should I do? Are there any auxiliary fuel vents?

If the blockage doesn't cause an engine failure, how would one know that such a blockage exists?

Cessna 172 fuel tanks are vented on the left side through a port, and the caps are also vented. The tanks are interlinked as long as the fuel selector is set to both, so a vent blockage on one side should not cause a vacuum. This makes a tank vent issue very unlikely, but still possible.
If all three vents were to become blocked there's nothing you can do about it, as the fuel caps are on the top of the wing you may not even realize there's a block at all until your engine quits due to fuel starvation. If you do suspect your vents are blocked you should declare an emergency and start looking for a place to land.
Keeping in mind vent blockage is very unlikely, if you have a reduction in engine power you should follow procedure, i.e. fuel pump on (not applicable to the C172 but you should memorize it anyway), carb heat on, fuel tank change (again not generally applicable to the C172 as most of the time you'll be set to both but still memorize it), check mags are set to both, mixture rich, etc.

As I recall, the right fuel tank cap is vented. The left is not. There's a diagram here: https://aviation.stackexchange.com/a/5161/520

I think it's model dependent, that post talks about the C172N, IIRC in the S model POH it says both caps are vented. In any case it doesn't change the answer.

That could be. The diagram is for the C172N, I flew the C172P and from my memory looks identical. They could easily have changed it for more recent models.

It could also be long range tanks versus short range too.

The fuel pump would depend on the engine type. I have flown C172S with fuel injection and those have an auxiliary fuel pump.

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text:
How do I fix a slipping throttle friction lock in my C182?
The throttle friction lock in my C182 works poorly in cruise, it slowly eases out to a lower power setting. What can I do to make it better? I've attempted to turn the lock nut harder but without result.

I suspect there is only one sensible answer to this, and that is to have a qualified mechanic check/replace as necessary.
To continue flying in the meanwhile I would add a check for throttle friction to my FREDA check which you probably already do every 6-10 minutes during cruise.

The throttle system is a metal plunger connected to a cable that pushes and pulls the throttle control on the carburetor. The friction device puts pressure on the metal arm of the plunger, usually using a set of pins which get pressed against the plunger as you tighten the nut. If the pins get worn down or the threads get loose you won't get sufficient friction to hold the plunger in place. I've never seen repair parts for these, you replace the entire throttle cable assembly.
You may be tempted to increase the friction available by wrapping the plunger arm with some sort of material. Do not do this, whatever you use could easily get caught and jam the throttle.


text:
How high could Concorde potentially reach by going fast and pulling up?
If Concorde was travelling at mach 2 and FL 600 then pulled up, it would enter a trajectory that went above its normal flight altitude before diving back down. I assume that it couldn't pull up to full control surface deflection in those conditions without the wings folding, so without damaging anything, how how high could Concorde go using this method? Is there a way to calculate/estimate this, or is it only provable by testing? I've searched google for answers but I can't find anything on this subject.
(An unrelated question that I couldn't find an answer to: what was the structural G limit of Concorde at cruising speed)

Testing was done 4 this sort of thing in the 50s by Chuck Yeager using an F-104 with a booster rocket under the tail. It would do ballistic arcs from its service ceiling up to about 100000 ft+, helped along by the rocket. It needed nose attitude thrusters to control pitch attitude above about 90000 ft because the flight controls had insufficient dynamic pressure to work normally. In The Right Stuff, the bit with him spinning out and ejecting near the end of the movie was about that last one of those tests where it almost killed him when it stalled and spun on "reentry" because the att was off.

The part about structural limit can form an entire question by itself and could be asked separately.

you may be interested by the part about energy convertion of how it flies. You are looking for zoom climb and transformation of kinetic energy to potential energy

There are a couple of ways to look at this question. The easiest is using first principles.
Therefore imagine that Concorde (flying at Mach 2 at FL 600) can, suddenly and without energy loss, pull up, such that it flies for example 10 degrees upwards. Also we assume the following:

The engine flames out immediately, therefore no engine thrust
We neglect air resistance

How much higher would it go? The formula to calculate this is surprisingly simple:
$$ \Delta x = 1/2 \cdot \frac{(V_I \cdot sin(\gamma))^2}{g} $$
with $V_I$ being the inital velocity (590 m/s which is Mach 2), $\gamma$ being the climb angle and $g$ being the gravity of $9.81 \frac{m}{s^2}$.
I have calculated it for a couple of angles:

$\gamma = 10°$: 535m
$\gamma = 30°$: 4436m
$\gamma = 45°$: 8871m
$\gamma = 60°$: 13307m
$\gamma = 90°$: 17742m

That gives us a first guess, but the question remains: Could it pull up at this high altitude? The answer is: Yes. Consider the formula to compute the dynamic pressure:
$$ q = 1/2 \cdot \rho \cdot V^2 $$
Concorde takes off at around $113 \frac{m}{s}$ at an air density of around $1.225 \frac{kg}{m^3}$. The air density at FL 600 is around 1/10th of the air density at sea level. However the cruising speed is roughly 5.2 times faster, which yields 2.7 times higher dynamic pressure at that altitude. Thus, the rudders definitely work at that altitude.
The real limiting factor here is the structural limits when you try to pull up at Mach 2. For example if you try to pull up your aircraft at Mach 2 with a constant acceleration of 1 G, you will follow an circle with a radius of ~50km. Even with 3 G acceleration, you will still follow an (upward) circle with a radius of roughly 16km. My guess is that Concord can safely handle around 3 G (for example, to be able to handle gusts at altitude). Additionally, you will lose a lot of your energy while pulling up, due to additional drag (remember, because of the increase angle of attack, the aircraft has more drag) and of course you are getting slower as you trade velocity versus height. Thus at some point you will not be able to pull up any further because you lost too much speed. I tried to estimate how much higher you would have to fly in order to go down to stall speed¹, and my result is 11.2 km of additional height. That would mean that you could reach a $~70°$ climb. However I neglected air-drag etc. and the fact that you will definitely not pull 3Gs at stall speed.
To get a definite answer, one would have to perform some computer simulations. Perhaps one of the popular flight simulations can help. But I would guesstimate, that at FL 600 going at Mach 2, you can probably (safely) pull the airplane up into a climb of around $\gamma = 30°$, which would yield around ~4.4km of additional height.
P.S: However the assumption that the engine will flame out at higher altitudes is probably true. My guess would be that the engine was designed such that it can not substantially exceed FL 600. But that is speculation.
¹ I simply assumed that the stall speed is at the same dynamic pressure as at take-off condition. This yields a stall speed of $357 \frac{m}{s}$.

In a 3g pull-p the induced drag during the maneuver will be about 9 times higher than in straight flight. Even with engines running, the Concorde will drop to subsonic speed quickly. Also,  as far as I remember, the g limit in cruise was lower than 3g.

Ah cool, how did you compute that? Perhaps We can calculate a more accurate answer?

Well, you could take into account that $g=9.75$ at $17742 m$ :-)

Let's have a look.

If its normal supercruise was M 2.04 at 60,000'

And it had excess power available (it did-dry and in addition had    reheat available)

And its aerodynamic capability was quite a bit higher than its       normal service Mach number (it was – Concorde 101 flew at M 2.23 or    1,450mph)

One could easily posit a test scenario in which a gentle climb was initiated just by selecting an altitude on the autopilot.
The autothrottles would do the rest in terms of power. Climbing at a steady Mach 2.0, Concorde could likely gain a significant amount of altitude. Perhaps 5-10,000' very quickly.
But before we go any further, we need to clear up some definitions to address some of the other comments.
The term 'ceiling' or ‘service ceiling’ in a normal aircraft refers to:
The density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude and with all engines operating and producing maximum continuous power, will produce a given rate of climb. A typical value might be 100 ft/min (0.51 m/s) climb, or on the order of 500 ft/min (2.5 m/s) climb for jet aircraft.
Normal airliners don't operate at their service ceiling, as this requires max continuous power and that is just a no-no for fuel burn. Also, you can get very dead, as the Pinnacle Airways CRJ-200 crew did by playing at the aircraft's service ceiling. You are at the edge of the aircraft's aerodynamic performance.
The service ceiling of 60,000’ commonly listed for Concorde, does not meet the normal definition as 60,000’ was its normal planned cruise altitude.
It is more than likely that its actual service ceiling 'hard limit' was quite a bit higher than 60,000' as Concorde cruised at 60,000' every day for 27 years.
I know, I flew on her in 1999 JFK-LHR.
The 60,000' certification service limit was (I believe) derived from a window loss scenario. If one window was lost the ECS could maintain cabin pressure until the aircraft descended to 10,000'.
Remember at 60,000' the TUC is a couple of seconds, and you require positive pressure breathing.
As to speed, the service speed limit for Concorde was a heat limited-127C. On my flight we reached 1,350mph and the nose probe read 126C (Yes, I spent about half an hour in the flight deck talking shop with the pilots and the very busy Flight Engineer) As mentioned, in testing Concorde ran out past M 2.23 but for service life reasons, its service limit was 2.04.
With the available excess power, a climb could be made while maintaining M 2.0-2.04. No sudden pull up required. At that speed, your climb rate at even a shallow angle is going to be impressive.

Might be better worded as, "Concorde routinely cruised at 60,000'" which is probably what you meant. I have read various accounts that it cruised between 55,000 and 60,000, for example in this answer.  Not doubting that you were on a flight that cruised at 60,000, but I wonder what percentage of the time that occurred and what were the reasons that determined the altitude, although presumably it was for many of the same reasons as subsonic aircraft such as winds aloft.

At 60,0000’, I would expect the Concorde might be cruising at the edge of its performance limit.
If you try a "zoom climb" with any aircraft at the edge of its performance limit, the aircraft might be dangerously close to the stall speed.

At 60,000 ft in standard atmosphere, Mach 2 is about 1147 KTAS and about 353 KIAS, which is lower than one might think, but not near stall speed yet. In fact, Concorde first slowed down at 60,000 ft (I forgot to what speed exactly) before actually starting to descent.

To really answer the question, you should provide figures. Otherwise, I fear this is more a comment than an answer. E.g. you can add energy consideration (how much kinetic energy when cruising at 60000ft, and therefore how much height gained when transforming the kinetic energy to potential energy while slowing down to stall speed neglecting losses due to drag and gains due to thrust, therefore giving only a first approximation)

One would have to look at thrust available at 60,000 feet. At supersonic speeds, any maneuvering may produce huge amounts of drag,

This is called Coffin Corner, and doesn't sound very fun https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics)

@StuartBuckingham "Coffin corner" does not apply to supersonic aircraft. There are analogous limitations, but they aren't the same.

@pericynthion good point! I guess there is no critical Mach# when you're supersonic. What is the analogous "line" that forms the corner? Is it just available thrust?

Typically engine temperature limits


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Who pays for Rescue response?
When a plane has equipment failure, or any number of other issues, they may declare an emergency. Quite often, one result of that is that the fire and/or rescue vehicles at the airport will be dispatched to inspect for fire/hot brakes, perform emergency services, or other things for that plane.
Who covers the cost of that? The airline? The airport authority?
(Note, I am primarily interested in North American answers, but any will suffice)

It really depends, larger airports this is paid for by the airport, and by extension the landing fees it charges, along with other fees collected by the airport from the airlines/passengers. This can be augmented with local/federal funding and taxes. Some services are paid for by the airline or its insurer (like wreckage removal). Off field services can vary even more.

The emergency services generally need to be on standby at the airport anyway, so it's not clear to me that there is even a particular cost for something like that unless it starts causing overtime or consumables like water/foam are used.

@RonBeyer That looks amazingly like an answer. And yet it isn't one.


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Aerodynamics of lift
How can lift on a canvas covered airplane wing in level cruising flight be explained without introducing Bernoulli ? Both upper and lower surfaces are bulged out,which indicates lower than ambient static pressure on both surfaces.

Do you think the pressure is the same on both sides?

Well , the pressure on the top surface is obviously less than that on the bottom, or the wing would not support itself but the average light A/C pilot has the impression that the below-wing pressure is higher than ambient static , I think , in this scenario——and that is not true

Simple, the lower surface is NOT bulged out!

I am not sure if I got your question completely.
As I am not entirely sure what you mean by leaving out Bernoulli.
Let's start with the lift issue:
Lift is created when the pressure (-forces) on the upper wing surface (suction side) and the pressure (-forces) on the lower surface do not cancel each other out. Usually this means that there is a net-force pointing upward (in level flight). Lift is therefore not directly connected to the ambient pressure. Does this answer the lift part of your question?
Image taken from wikipedia

Now let's focus on the bulged out surfaces:
I would guess there are at least two effects:

As you can see from the picture above the pressure is lower (than ambience) on
pressure and suction side (but since the pressure on the suction
side is lower than on on the pressure side, there is a net-force
(lift)).
Depending on the aircraft, it could be that the high-pressure in the stagnation point of the wing or aircraft pressurises the wing and cabin which would increase the effect from above. A bit like the canopy of a paraglider.

Your observation is correct. There is suction (= lower than static) pressure on most of the surface area of both sides of a wing. The reason is simple: The wing has a certain thickness and needs to push air aside in order to move through it.
In order to make way for the wing, the air will accelerate when flowing over the wing, so an imaginary parcel of air will be stretched lengthwise, becoming thinner in the process. The suction on both sides of the wing is doing this stretching, because it pulls the oncoming air in. Air is accelerated over the forward part of the wing and decelerated again as the airfoil thins down over its rear portion.
The air inside the wing is sealed by the airtight fabric and has about static pressure (what you would measure with a barometer when at rest). Consequently, the lower air pressure of the accelerated air on the outside allows the air on the inside to push the fabric out.
That lift is created at all is caused by a pressure difference between the convex upper surface and the flatter lower surface. Suction is higher on top than on the bottom.

The "suction" aspect of lift where Bernoulli gets involved is just a small part of it.
Lift is generated by deflecting air down, or more correctly, inducing a large air package above and below the wing to move down.  A flat sheet of plywood makes lift.  The biconvex supersonic airfoil on an F-104, being more or less a flat sheet of plywood with sharp edges and a bit of surface curvature, makes lift.  The completely flat surfaces of almost all fabric covered tails of light aircraft make lift (downward).  They all do it by deflecting or inducing air to change direction.
The lift is the action/reaction created by the downwash generated by an airfoil inducing air to move from here to there. A helicopter hovering is not being suspended just by a suction force being created by the low pressure area above the blades.  It's being suspended by a the mass of air being accelerated down by the rotor's moving wings.  Not much different from a hovering rocket.
The airfoil shape just makes the wing do a much more efficient job than a flat sheet of inducing air to move down because of the pressure distribution. A flat sheet redirects mostly the air below to move down and just a little bit of the air above.  An airfoil is able to influence a large package of air above to move down as well.  The low pressure region is creating a bit of a suction effect that acts upward directly on the wing, but at the same time while it is sucking the airfoil up, it is also sucking some of the air package above it down, and the downward induced movement of the total air package is the bulk of the lifting force.

I am not sure if I can follow your explanation. Which force is deflecting the air? Even a flat plate with an angle off attack has a pressure and suction side. To separate deflection and pressure from each other over-simplifies the physics.

As I said, the airfoil induces a large parcel of air to move down both below and well above."Deflection" is just a shorthand.  But it's the Newtonian action reaction of the air parcel being moved that is most of the lifting force.Air that was here was moved down to there by the passage of the wing.  You know, downwash.  "Suction" from the Bernoulli pressure differential is just a part of it and explaining lift purely as Bernoulli generated pressure differential is the over-simplification.It doesn't explain how a flat sheet with no curved upper surface can still make lift, albeit not very well.

If you are talking about a fabric-covered wing like that on a Piper Cub, the flow of air over the wing is not what determines the shape of the wing: the fabric is tightly stitched to the ribs, spar(s) and the leading and trailing edges, which themselves are made of solid material. That "skeleton" structure is what gives the wing its shape.
The fabric is also painted with a sealant (commonly called "dope") which makes it impossible for air (or water) to flow through the fabric. This means that any pressure distribution which develops across the outside area of the wing will be transmitted as a force from the fabric to the underlying structure of the wing and ultimately to the main spar as lift.

Notice the diagram above is correct for low angle off attack, creating downward "lift" that will bulge fabric down as well as upward lift bulging the fabric up.  This is because static air inside the wing has higher pressure than both.  More lift up so net lift is up.  As AOA increases, we may see loss of "bulge" on bottom, but as you say, a well made wing is tightly stitched.


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What aircraft has a single constant orange light?
I live under a fly path in Oldham near Manchester and I see planes passing by every day/night as they approach the airport. However today around 21.20 I have seen something different too.
A plane just passed above our house to start its approach to Manchester then when it was further away roughly above Ashton-under-Lyne I noticed a contrast single orange light passing above the house.
It was somewhat higher than the passenger planes around this area and it's travelled with constant great speed. I followed with my eyes until it's disappeared on the horizon above the peak district (took about 1.5-2 minutes). It's travelled in a direction about SSE (roughly towards London). I couldn't find anything on the Internet suggesting anything flying with constant orange light. BTW it had no sound whatsoever and it wasn't showing up on flight radar either as I checked that straight away. I do not drink and do not smoke funny things. Any idea what this could be?

How could you tell that it was higher than the passenger planes in the area?

Judged by my eye. Passenger planes approaching MAN airport flying only 3-4000 ft above. And this could be somewhere around that region too but seemed to be a bit higher than approaching aircrafts in the area.

From your description it sounds more like the International Space Station than an aircraft. That looks like a small orange or yellow light because it's the reflection of the sunlight For that reason you're most likely to see it in the hour or two after sunset, and it's clearly visible with the naked eye in good visibility. It's much higher than aircraft and takes about 90 seconds to travel horizon to horizon. Obviously you won't hear it or see anything on aircraft tracking sites.
That said, ymb1 suggested looking at this ISS tracker site. Assuming your 2120 was in British Summer Time (UTC+1), the ISS would have been somewhere over the South Pacific Ocean at that time, which would rule it out.

I've seen the ISS passing by quite a few times but that is obviously "flying" way much higher than this blob did.As I just commented on the above for ymb1 (judged by my eye) this thing seemed to be flying just a touch higher than approaching aircrafts for MAN airport. Those approaching in the altitude 3-4000 above us. I also thought it was maybe a drone, but even drones would have flashing lights on and the speed was just very fast and obviously as it disappeared on the horizon remote control would be an issue. (unless it would have its own satellite navigation)


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How can Schrenk approximation be used to model lift load on a rectangular wing?
How can I use Schrenk approximation to calculate load distribution on my rectangular wing?
A worked example will be appreciated.

NASA has a report on it: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930094469.pdf


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Where is the compression on a compression strut in a tube and fabric airplane coming from?

I understand the functions of every part of a tube and fabric (two spar) ultralight wings and the loads they carry but what keeps puzzling me is the compression strut of a two spar wing as seen above.
My question is where is this compression on a compression strut between the main and rear spar coming from? Is it from the drag and anti wires, the spars itself, where and how do you calculate this conpression force?

They are called compression tubes because they are under compressive load at all times in the wire braced ladder truss formed by the spars, compression tubes and cross bracing, whereas other members can be under tension, or compression, or unloaded, depending on whether the drag loads are from the front or the back (anti-drag) (back mostly in the theoretical sense, although you could have reverse loading in the right flight conditions - and the drag wires need the anti-drag wires there to absorb their pre-tension to hold everything square when it's sitting on the ground).
The compression tubes are under compression by the tension of the cross bracing wires when at rest.  In flight, they are also in compression, transferring the drag loads from the first bay's drag wire to the next bay's drag wire.
I've tried to colour code the loads in the diagram.  The green wires are called drag wires, the red wires are called anti-drag wires.  In forward flight, the green wires will be in tension and the red wires unloaded, and the compression tubes in compression.  In "backward flight" (say in a tail slide), the red anti-drag wires will be in tension and the green wires unloaded.  At rest, the wires are equally loaded with a pre-tension to keep everything square.  But in the drag, anti-drag, or at-rest case, the compression tube sees only compression load.
Theoretically, you could attach the compression tube to the front and rear spar with just a locating pin sticking out the ends that fit in holes in the spars, because the tube connections to the spars never get "pulled on"; they are always being pushed.  On some fabric airplanes the connection is not much more than that; maybe just a threaded pin that goes through the spar with a nut on the other side to hold it in place before the wires are tensioned.

Ideally, the cross bracing has only very little tension so the wires can take up all the shear load for which they are really there.

You want a nice, taut fabric cover on this wing, don't you?
The main function of the compression struts is to keep both spar tubes from being pulled closer by the fabric cover. Of course, Niels is right, aerodynamic forces come on top of this and will also pull on the tubes in the wing's plane.
In order to calculate those forces, integrate the tension in the fabric over wingspan when loaded by maximum lift forces. Below I have sketched those lift forces – they want to pull the fabric up, increasing tension within it and so the compression forces on the struts.

I hope I got the basic structure about right. Please correct me where needed.

During flight, a forward-pointing force must be applied to the leading edge of a wing in order to push it through the air against the drag force that the air is applying to the wing, and to prevent the force of the onrushing air from crumpling the leading edge backwards. The purpose of the compression strut is to convey that force from the main spar to the front edge of the wing, which appears as compressive stress in that strut.

The cross wires are the clue: they are under tension, and the compression bar neutralises the pre-tension forces.
This arrangement transforms the construction into a geometrically defined structural shape that can absorb the bending moment of the wing.


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How much time does it take to calculate the leveling and weighing of big and small aircraft?
What methods are used to achieve that?
According to my search :

For old planes they use a plumb bob and measuring tools.
On new and big planes, the process is computerized. Built-In Electronic Weighing like the Boeing 777

The calculation just takes a few minutes. It's the setting up that takes the time. Usually, though, this is done (or at least used to be done before I retired in 1999) as part of a maintenance check so it's hard to separate out the time used just for the weighing part. Also, if you brought an airplane in just for that, the elapsed time required would vary depending on how many people you put on it. I once watched them put a 747 up on jacks to cycle the gear. That took a little over an hour from start to finish. You'd want to add a little more time to that for recording readings.

thanks :) i hope to know the time including the equipment  setup  ?
and is the process automated now or no

I'm 16 years out of date now, so I can't address how automated it is now. In my previous comment, I forgot to say that you'd also have to add in the time required to empty the fuel and remove items not to be included in the empty weight. However, if you knew accurately how much fuel you had and the weight and location of items, you can account for them that way.

The frontier between old and new aircraft is not that clear. The B777 is not really a new aircraft as its maiden flight took place more than 20 years ago (in 1994).  You may also specify what "big planes" means for you (I could be airliners designed for more than 50 passengers)

Having recently weighed my plane I can tell you what's involved for determining the Basic Empty Weight for a small aircraft:

The aircraft equipment list is checked and updated.
This is kind of important as the equipment list includes the weight and arm of everything installed on the airframe. If this list is not accurate future weight and balance updates based on adding/removing equipment using the weights and arms on that list will be incorrect, and your computed weight and balance will start to diverge from the actual weight and balance until the plane is weighed again.
The aircraft interior is cleaned to "factory empty" status.
Pens, pencils, 3-year-old charts, note pads, and other things not on the equipment list are all removed, and things like tow bars are placed in their appropriate location/holder.
The aircraft is serviced with "fluids" per the manufacturer's procedures for weighing.
For most small planes this means de-fueled, full engine oil, & full hydraulic/brake fluid.
The shop sets up and zeros their scales.
You tow/push the aircraft onto the scales.
(Or lift it on jack stands with integrated scales designed for this purpose.)
The aircraft is leveled on the scales.
The plane must be leveled laterally (left-to-right) and longitudinally (nose-to-tail), otherwise the computations made later will be inaccurate.
The numbers on the scales are recorded.
The Weight and Balance is determined:

Add the numbers from all scales used. This is your Empty Weight.
You do some math on the scale numbers to determine the Center of Gravity.
(Since you know the station/arm of each scale you can figure out the CG based on the weights)

As Terry mentioned, setting up took more time than the actual weighing and calculations. In my case I spent about a day straightening out the equipment list, and the shop that did the weighing spent about 20 minutes verifying that I hadn't missed anything. Defueling the aircraft adds a significant amount of time to the process as well. Moving the plane onto the scales and leveling it took approximately 15 minutes, and doing the math took maybe another 5 minutes.

On larger aircraft the same general process can be used with larger scales (or jacks) - load cells integrated into a taxiway or ramp area are another option for doing this.
I'm not sure if aircraft that can determine their operating weight (by load cells installed in the gear assembly) can also determine their own empty weight - I know the weighing report I received includes calibration information for the scales used, so presumably weighing a large aircraft using its built-in load cells would require those cells to be properly (traceably) calibrated prior to using them for this purpose.

thanks for sharing your experience that's a great answer :)

Incidentally at least for the PA-28 there's no plumb bob involved for leveling: you use a regular bubble level. There are two screws on the fuselage that come out for leveling it longitudinally, and for leveling laterally you put the same level on the spar box (the maintenance manual includes pretty pictures). Procedures for other aircraft may vary, but they'd be detailed in the maintenance manual.

Related: How does a commercial airliner measure its weight/mass?.


text:
For a modern Turboprop/Jet will going at 300/400 mph TAS at 10000 feet require more thrust/use more fuel per unit time vs going 600mph at 30,000 feet?
My understanding is one of the primary reasons why modern planes Cruise at around 30,000 to 40,000 ft is because of the lower air density less results in less drag. So for a given thrust, an airplane can fly faster in the higher altitude ...
However, how does fuel efficiency figure in ? To generate the given thrust does the plane require less fuel? Use a simplified toy example (Scenario A) to At 300 mph True Air speed. At 10,000 ft. Versus flying at 600 mph at 30,000 ft. Will flying 600 mph at 30,000 ft require both less thrust and use less fuel per unit time versus 300 mph at 10,000 ft, ?
Or (Scenario B): Are talking about requiring less thrust and less fuel per unit time for equivalent  Air Speeds at different altitudes? That is, is flying at  300 mph at 30,000 ft requires less thrust and consumes less fuel per unit time than 300 mph at 10000 ft (assuming 300 mph is sufficient  speed to generate lift at that altitude of 30000 ft of lower air density). Let us ignore like jet engine efficiency for now at given altitude, And just focus on drag drag, thrust and fuel consumption...I know modern engines are also optimized to work at certain altitude window etc
Actually it occurred to me I may have got it all kind of backwards. The Same amount of thrust at a higher altitude translates to greater True air speed- due to lower drag due to lower air density at higher altitudes. This means you cover more distance for same amount of fuel! It is fuel per unit distance (miles per gallon) that is reduced, not fuel consumption per se (Liters per unit of Thrust). Is this on the correct track?
it Scenario A while going 600 mph at 30000 feet at constant thrust may use similar fuel per unit TIME vs 300 mph at 10000 feet, it will likely use less fuel per unit DISTANCE traveling greater distance per GALLON not necessarily per unit TIME. As for Scenario B: Obviously going 300 mph at 30000 feet (assuming 300 mph is sufficient to generate enough lift at 30000 feet with lower air density) will use less fuel per unit time and require less thrust than going 300 mph at 10000 ft (due to lower drag due to lower air density at higher altitudes) Is this understanding correct track?

Actually it occurred to me I may have got it all kind of backwards. The Same amount of thrust at a higher altitude translates to greater True air speed- due to lower drag due to lower air density at higher altitudes. This means you cover more distance for same amount of fuel! It is fuel per unit distance (miles per gallon) that is reduced, not fuel consumption per se (Liters per unit of Thrust). Is this towards the correct track to answering my question?

You can just delete the bold-text part. There's no need to add every version and edit or change in your post.

There are a lot of competing effects that depend on a lot of details.  This makes it very difficult to give a short (correct) answer.
Instead, I'll present a set of figures from some calculations I've done on an aircraft meant to be similar to a typical large transport aircraft in service today.

The chart of most interest to you will be the 3rd on the bottom row.  The aircraft's Specific Range (SR) is the fuel economy in terms of distance covered -- the units here are nautical mile per 1000 pounds of fuel.
As you can see, this aircraft's best range is at 36,000 ft and about Mach 0.85 -- where it gets about 16 nmi/1000lb.
The bold line in each chart represents the zero specific excess power line.  That is the boundary of the flight envelope -- the aircraft can not fly in steady level flight outside this boundary.
Also of interest is the 2nd chart on the bottom row.  The aircraft's fuel flow (wdot_f) is the fuel consumption in terms of time aloft -- the units here are pounds per hour.
As you can see, this aircraft's best fuel flow is between 20,000 and 30,000 lbm/hr.  The chart doesn't have enough contours to really pick out a precise optimum value.  However, we can see that you can achieve better than 30,000 lbm/hr from sea level until 40,000 ft -- so long as you carefully choose the correct airspeed for each altitude.
The figures on this chart are:

Lift to drag ratio (L/D) which is dimensionless

Used to optimize glide distance.

Power off rate of descent (RoD) in ft/s

Used to optimize glide time.

Specific excess power (P_s) or rate of climb in ft/min

Used to optimize climb time.

Climb angle in degrees

Used to optimize climb distance (obstacle avoidance).

Fuel specific climb (f_s) in ft/lbm

Used to optimize climb fuel consumption

Fuel consumption (wdot_f) in lbm/hr

Used to optimize flight endurance

Specific range (SR) in nmi/1000lbm

Used to optimize flight range

True airspeed (V_t) in kts

Used to help convert these charts from Mach to kts true.

Calculating these charts requires a drag model of the aircraft that includes effects of compressibility.  It also requires an engine thrust and fuel flow model that includes the effects of speed, altitude, and throttle setting.  It also requires a standard atmosphere model that includes the variation of pressure, density, and temperature with altitude.
Some information about the aircraft is also required.  Most importantly, the wing loading and thrust to weight ratio.  Some other minor assumptions are required.  For example, in this case, a gross weight at the middle of cruise (about half the onboard fuel has been burned) is assumed.
At every point in the flight envelope, the drag is calculated.  Then, the appropriate throttle setting for each chart is determined -- for the gliding metrics, zero throttle -- for the climbing metrics, full throttle -- for the equilibrium metrics, throttle that gives thrust equal to drag.  Once the throttle setting is known, the TSFC can be determined and the rest of the computations can proceed.


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Why does flying at higher altitudes generally improve fuel efficiency for commercial airplanes given Specific Fuel Consumption rate (SFC)?
I’m a high school physics student with an interest in aviation and would like to understand why commercial airplanes fly at high altitudes (e.g., 35,000 feet) to improve fuel efficiency. My understanding is one of the primary reasons modern commercial planes fly so high (35000 feet at Mach 0.85) is because at higher altitudes due to less dense air there is less drag. Which means for the same amount of thrust you can fly faster (here talking about true air speed or ground speed). So far am I being clear?
Lets use some hypothetical numbers in a toy example. Let us say for the same amount of thrust (300 kN HYPOTHETICAL toy number) a airplane can go 400 kmph TAS (assume same as ground speed)  at 15000 feet, but  for  the same 300 kN thrust can go 800 kmph at 35000 feet. Let us say the airplane has to cover a distance of 1600 km. The plane at altitude 15000 feet can cover this distance in 4 hours while the plane at 35000 feet in 2 hours. How does this help fuel efficiency (in terms of Liters/km, gallons/mile)?
To generate the same amount of thrust (lets say 300 kN as a toy number) requires a certain number of fuel consumption rate (g/second Liters/Minute.)... I think the amount of thrust you get for a specific fuel consumption rate is called the Specific Fuel Consumption (SFC) which is the inverse of specific impulse (isp). I realize at higher altitude the density of fuel changes too this affects consumption, but let us assume they are approximately equal..i.e approximately same fuel per unit time is consumed to generate the same amount of thrust (300 kN) whether at 15000 feet or 35000 feet. That is for the purpose of this question I am assuming TFSC remains relatively constant with altitude.
Since the plane at 35000 feet will cover its 1600 km trip in less time based on its speed of 800 kmph it will have to maintain the 300 kN force for less time,  leading to less fuel consumption, leading to less fuel per distance (kg/hour, or Liters/Km)? In other words, if the airplane at 35,000 feet needs to maintain 300 kN thrust for less time to cover the same distance, does this translate to lower fuel consumption per unit distance?
This  is a highly simplified but is this approximately on the correct track (I made an assumption of constant fuel consumption rate at different altitude,ignored things like engine efficiency improving at higher altitude compounding the gains, and probably many unstated assumptions..)?

It is similar but not the same. It touches on TSFC, but assumes for this question it remains constant  with altitude (while acknowledging in reality it probably doesn't, and TSFC actually improves, further compounding gains in fuel mileage). It is a more basic question.

The atmosphere gets colder up to about 11km (36,089ft).  From there, the temperature stays the same for quite a while (in airplane terms).
Because the input air is colder, the engine can add heat more efficiently -- and add more heat before reaching the engine's maximum temperature limit.
This results in the TSFC (thrust specific fuel consumption) of a jet engine scaling with the square root of the temperature ratio.
$\mathrm{TSFC}=\mathrm{TSFC}_0 \sqrt{\theta}$
Where
$\mathrm{TSFC}$ is the thrust specific fuel consumption at altitude
$\mathrm{TSFC}_0$ is the $\mathrm{TSFC}$ at sea level
$\theta=T/T_{sl}$ is the temperature ratio at altitude to sea level.
So, $\mathrm{TSFC}$ gets better as long as the temperature drops (until 36,000 ft) and then it doesn't get better anymore.  This is why most transport aircraft fly at this altitude.

Here is a simpler way of thinking about this, in which Rob Mcdonald's correct answer is deeply embedded.
Flying higher means less drag, so you go faster on the same amount of horsepower. This means less time spent in the air with the engines burning, which means better fuel mileage and lower costs.
But flying higher also means less air to burn your fuel in, which means less horsepower. But if your engine has a big compressor in it, it has the capacity to jam more air into the engine despite the altitude and thus full horsepower is maintained at high altitude without running the engine past its maximum temperature limits.
There comes a point however when the big compressor is no longer capable of keeping up with the thinning air and flying above that altitude causes a loss of engine power, and the plane therefore loses speed as it gains altitude. So you add pitch-up trim to make the wings generate more lift for you, so you can climb into less-draggy air and counteract the fact that you are going slower.
Finally there comes the point where the wing is pitched up enough to be on the verge of a stall and the engines cannot develop enough power to fly any faster to escape the stall, and at that point you are mushing along as economically as possible. At this point the only way to add altitude is to decrease the plane's weight, which it does by burning off fuel. So, on a long flight you gradually add altitude as your weight goes down and thereby seek out and hold onto the max economy condition for as long as you can, all the while watching your engine temps.
The fact that all modern airliners have very similar max economy points is because they all use more or less the same engine technology.
Finally, note that it costs extra fuel to hoist a plane high into the air, and you have to make up for that fuel cost by cruising at max economy for a certain duration. There may not be enough flight time available at max altitude to pay for the climb, and so for any stage length there will be an optimum (lowest overall cost) cruise altitude which will be lower for shorter flights.
Since those short flights do not require a 40,000 foot cruise, they are serviced with smaller planes that fly lower and slower.


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What are the areas marked in green around the taxiways?
In the photos for this AvHerald article you can see areas marked in green with yellow stripes around the taxiways.

The entire maneuvering area appears to be solid concrete. The green painted areas are outside of the taxiway edge markings and the vehicle roadway markings. Is this green area intended to be a buffer zone to account for wings sticking out past the taxiway edges? Or is it just there to help show where the taxiway edges are? Should an aircraft's wingtips remain within the taxiway or can they hang over the edge?

Are you sure you linked the right AVHerald article? The one you linked is about a crash in the air, not a ground collision... I think you meant to link this one

@RonBeyer You are correct. Fixed

It's essentially "fake grass" -- a "no taxi" / "no drive" area, the same as real grass would be.  The concrete may very possibly be stressed to support the full weight of big aircraft, and the areas are painted that way simply as a matter of keeping traffic flow in the designated areas, although it's possible that some areas marked that way may not be in a condition that you'd want to taxi on them.
As far as emergency vehicles go, they have permission to do whatever they need to do when responding to an emergency, which includes driving on anything they need to.  And the people driving the fire trucks will be well aware of any parts of the tarmac that even they need to avoid -- but if it's even close to being able to support an aircraft, it'll support a fire truck just fine.
More than anything else, though, it's a matter of marking the ramp to designate the "don't taxi here" areas from those where you can taxi.  Often, separating a ramp (taxi more or less at will) from a taxiway (ATC clears you where to go, and it's obvious where aircraft will be entering/leaving the taxiway).  (As the overhead image shows, wingtips can & do extend over the green areas; adjacent taxiways separated by such areas would be laid out so that aircraft on respective centerlines would have whatever wingtip clearance is required.)

What do you do if you really want a grass surface then? (Say, if you were toodling along in a Tiger Moth with a tailskid instead of a tailwheel...)

@UnrecognizedFallingObject According to one old Moth pilot I've talked to, you would just fly above the taxiway at about 35Kt and 5 feet AGL. (No problem doing that - it's well above the stall speed!) When you get to where you want to be, land again.

@UnrecognizedFallingObject  Umm, don't land at LAX?  Actually, there is some real grass there; north of 24R iirc, and in the overhead photo there seems to be some south of 25R (i.e. between 25L and 25R). Of course, that would be landing off of the runways there, which goes back to the first point.  Or, being where LAX is, there is also the beach immediately west of the runways...

@RalphJ " Umm, don't land at LAX" - My old Moth pilot had some stories of the time (1950s) when you could radio London Heathrow and request to land, take on 2 gallons of fuel, pay for it in cash, and depart - and be taken seriously! (But that guy didn't bother with the main runways - he just landed on the taxiway as close as possible to the fuel bowsers, and took off the same way)

@TomMcW, you should ask that as a separate question.


text:
What were the advantages of the L-1011 AoA sensor design?
The Lockheed L-1011 had an unusual type of AoA sensor. Instead of the usual vanes it used a tube with two rows of holes in it about 90° apart. A diaphragm sensed the pressure differential between the two sets of holes and a motor adjusted the sensor until the differential went away. The AoA was them determined from the angle the sensor was to the fuselage.

 Source: NTSB accident report TWA 843
This seems particularly complex, requiring a motor and possibly introducing lag into the reading. Why did Lockheed decide on such an unusual sensor design? Does it have some a advantages to a conventional vane? Was it used on any other aircraft besides the L-1011?

You can make your own AOA sensor for your homebuilt airplane that way, using a fixed horizontal tube with the two rows of holes in an upper and lower chamber, and connecting each chamber to the pitot and static ports of an old airspeed indicator with the face redone with AOA markings.  You had to calibrate it yourself though.

Hypothesising: Maybe one advantage is that the moving parts, mechanics and electrical sensors are somewhat protected, given they’re inside the tube or even inside the fuselage?

Speculation: it's easy to detect faults. If there's a pressure offset even after you applied motor commands, then you know the tube is jammed. Likewise, instead of servoing for zero pressure difference, you servo to track a sine wave offset. If the tube is blocked, you'll quickly see the tracking error.

The X-15's nose mounted Q-ball alpha/beta sensor worked the same way (a servo system rotated the ball until the pressures were equal, and then the angle of the ball was read). It was hydraulically powered! Good diagram on p. 5 https://www.nasa.gov/centers/dryden/pdf/87711main_H-374.pdf


text:
What is the relationship between Angle of Attack and Induced Flow?

 (Image Source: Principles of flight. ATPL ground training series - Author: CAE Oxford Aviation Academy (UK) Limited 2014)

I'm studying the airplane's propeller. And I found this picture in my textbook.
I just can't figure out why they wrote 'TAS of aircraft + Induced Flow' here.
I’d really appreciate it if someone could explain the relationship between AoA and Induced Flow.
As I understand it, Induced Flow is the downward flow of air that's perpendicular to the direction of motion. But how can it affect the Angle of Attack?
I’d be grateful for any responses because I'm really confused. Thanks!

From another answer about propeller thrust, this was said: As this flow passes behind the propeller, the diameter of the induced flow is contracted and the flow velocity is increased by a factor of about two. This accelerated flow is the propeller slip stream.  Consequently, the discussion appears to be in regard to flow induced into the propeller disk by the propeller, itself.  This induced flow is particularly significant at the initiation of the takeoff run when thrust from the propeller is static and at maximum.

@Denis no worries. thank you for adding the source!

Just like for a fixed wing, also behind the trailing edge of a blade a wake is released which mainly possesses a downward movement, the so-called downwash.
But unlike a fixed wing, as soon as the blade makes a complete rotation around the hub, it bumps into its own wake; and, if there are more blades on the hub, then it bumps into their wakes as well. This swirling environment that a blade encounters in its rotation is what is called "induced flow" in your picture (aka "inflow") and it has a quite complicated nature:

Wake released by the propeller of what seems to be a Leonardo AW609 (picture source)

How can [induced flow] affect the Angle of Attack?

No matter how complicated it is, its main movement is downwards and results in a general decrease of the AoA seen by the blade, as depicted in your picture.

What is the relationship between Angle of Attack and Induced Flow?

Being so complicated, it is not possible to give a simple relation for the inflow. It can anyway be demonstrated that if the inflow remains constant along the bladespan then the drag associated to it is minimised: this is different than a wing where the induced drag is minimised if the lift along the blade is elliptical. The chord and the twist along the propeller are also chosen to try to keep the inflow constant along the span.

Just as there is downwash aft of a lifting wing, there is upwash in front. This induced flow in front of a lifting wing affects local angle-of-attack (e.g., just in front of the propeller plane of rotation) but not the true AoA of the aircraft through the air mass. Flight test nosebooms mounted in front of a nose or wing with angle-of-attack vanes have to be calibrated for upwash in order to give an indication of true AoA. The figure shown must be a top or bottom view and assume zero sideslip angle. Otherwise, the red line would not appear perpendicular to the blue line. Hope this helps.


text:
How high do they cut the grass on airports?
I've read that they try to keep it short. But on other sites and documentaries, it is said that they have to keep it long so that the birds don't look for food. Which is correct: short or long?

It depends on the type of bird and mammal species in native to the area and also the type of grass used in turfing; some of them may not survive if mowed very closely. FAA's Wildlife Hazard Management Manual concedes:

Species-specific responses may be expected.  ...  Airport managers
  need to work with airport wildlife biologists to determine what species of concern in regards to aircraft safety are in their area and what the habitat needs are for those species.

For most airports, FAA recommends a height of 5-8" of grass.

Considering bird, mammal and vegetation limitations, mowing at least monthly at a target of 5 - 8 inches may work in many airport environments as
  part of a wildlife hazard management program. ... Mowing at 5 - 8 inches should also reduce
  small mammal abundance.

You can find the link to the related Advisory Circular here: https://www.faa.gov/documentLibrary/media/Advisory_Circular/draft_150_5300_13a.pdf
See Page 101, paragraph B. Maximum of 6 inches in the runway safety areas.
Wildlife biologist generally recommend between 6 and 12 inches everywhere else on the airfield unless any haying will be done.

It is very important to authorities keep the grass cut, as we can see at Cork Airport (courtesy of youtube).
Doing this, the airport signs can be seen clearly by the pilots, avoinding mainly runway incursions, and also keeping far, as much as it can, the birds and their nests. This previous measure sometimes does not work as we wanted, but it might help a lot decreasing the bird hazardous airside.
After cutting the grass, the ground personnel will perform a runway inspection to clean it from debris.

So it is short or long? Could you please link to the video on YouTube in your post? Thanks.

This screenshot isn't "courtesy of youtube" -- the company doesn't create the content on its site. Please credit the original channel and make sure the licensing scheme on the video lets you share screenshots like this.

This answer does have a good point. Regardless of the height of the majority of the grass, and airport will typically cut the grass around signs and light fixtures very short, to keep them visible.


text:
What tests are done on aircraft wings for testing the effects of lightning?
During the testing phase of aircraft wings, there are lot of testing like temperature, pressure, humidity, vibration and load/stress. Apart from these, does any one have idea which other tests are done on them for complete qualifications like like lightning?

Your question is more applicable nowadays. 20 years ago, the airplane were enterely made of aluminium and were design to actually be a easy path for lightings as they were made of metal, the lighting was passing by. However, with the increasing composite composition of an airplane your question becomes really sensible where the lighting path goes though a composite not prepare for electricity (there are some tricks here...)

There is a difference between the title (only lightning tests) and the body (which other tests, like lightning). So are you interested only in lightning tests or any certification tests?

I have edited the question as other commented said apart from what all the categories I have said, only lightning is left. But if you know of any other tests, and if you explain them, that will be beneficial for everyone.

Almost all the tests done on aircraft wings can easily be categorized in one of the areas you mentioned.
The only remaining thing I can think is bending an aircraft's wing. It is stated on BBC as:

Many modern passenger jets can flex their wings nearly 90 degrees in a test rig.

For B787, it is reported:

During the test, the wings on the 787 were flexed upward
  “approximately 25 feet” which equates to 150 percent of the most
  extreme forces the airplane is ever expected to encounter during
  normal operation. The test is used to demonstrate a safety margin for
  the design and is part of the certification process to show the
  airplane can withstand extreme forces.

This video shows (also this one) how much force a wing can take before breaking.
OP asked about tests for lightning effects. Lightning commonly strikes the nose, wingtips, engine cowlings, and tip of the vertical tail. Hence, wings are not the only parts of an airplane which needs to be protected against lightning.
To avoid reinventing the wheel, please see the following questions:

How is an on ground lightning strike test conducted?
What happens when an airplane gets struck by lightning?

I would consider that part of the load and stress testing.

I am wondering what tests are done to check if lighting will affect the wings ?

@NitinG If you are talking about lighting on wings, please look at this question. However, I suspect you are talking about lightning.

@NitinG that's a good question. I believe those tests are done on the components and not the whole wing.

@NitinG If you're really asking about light(n)ing testing, then it would be best to edit your question and add that. It would make the question much more specific and therefore it would be easier to get a good answer.

Question edited but lightning is only one thing, any other tests are still done on them apart from what I have mentioned.


text:
What happens when lightning strikes an airplane?
What happens to an airplane when hit by lightning?

@Simon Umm not quite true - unclosed duplicates do. It can be argued that some dupes that redirect automatically are good for the site (more to search for). That said `@Pedro, your question is so similar, you could have found it in the search, and  it doesn't add any value to the site - it fractures the answers.

See also http://aviation.stackexchange.com/a/3833/1289

Since the aircraft is not grounded, the physics are the same as with a car that gets struck by lightning. The aircraft's skin will be charged, but very little current will be induced in internal parts in the process. The outer skin will act as a Faraday cage and protect the inner parts from the electric field.
This is greatly helped by a metal structure. Composite aircraft parts need a copper mesh over all external surfaces to give them sufficient electrical conductivity. The terminals of that mesh must be connected to the metal parts of the structure to make sure that all parts will have the same electrical potential in case of lightning strike.
However, the ionized air caused by lightning will leave burn marks on the surface, and an inspection of the affected part and the electrical equipment is advisable.

Comments are not for extended discussion; this conversation has been moved to chat.

The Faraday cage it right, but there is a big difference from the bird on a high voltage line. The bird gets statically charged, no current except for the small amount to create the charge. There is a huge current flowing through the Faraday cage.

@VolkerSiegel: Right, the current stays in the wire while the outside of the plane becomes a wire for the lightning. What happens on the inside is more similar. Could you propose a better analogy?

@PeterKämpf I notice that I missed minor, but interesting point about the bird: The current stays in the wire only when the resistance of the bird is much greater than the resistance of the wire. A car is the classical example for a Faraday cage. Otherwise, the physical cage itself.

@VolkerSiegel: Right, the car analogy is much closer.


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Aircraft lightning: What are the requirements for airworthiness?
Can you enlighten me about the airworthiness requirements in the field of lightning, for commercial aviation:

Which voltage or intensity is the aircraft required to sustain?
How is it demonstrated in practical?

Any major certification agency will be good.

Which country are you interested in?

@acpilot: EASA or FAA.

Are you looking for certification of the airframe, or airborne equipment?

@DeltaLima: Primary for airframe, e.g. does one test with some intensity between wingtip and nose, or does one submit the airframe to an electric field using plates, does one check if elevator hinges melt, etc.

When dealing with lightning protection, there are two significant areas that must be addressed: direct effects of lightning and indirect effects.
The FAA provides guidance on these two areas in the following advisory circulars:
20-155A - Industry Documents To Support Aircraft Lightning Protection Certification
20-136B - Aircraft Electrical and Electronic System Lightning Protection
The lightning zone analysis from the AC 20-155A will define the test requirements for the airframe and help determine the level of testing for installed equipment based on its location in the aircraft.
At the aircraft level it can be a very complex and drawn out process negotiating the specific testing required with the FAA. Once that is done, requirements and verification for the equipment can be developed.  A short summary of that process from AC 20-136B is:

6. Steps for Showing Compliance.
    a. The following seven steps describe how you may comply with 14 CFR
  23.1306, 25.1316, 27.1316, and 29.1316 requirements for your aircraft’s
  electrical and electronic systems:
  (1) Identify the systems to be assessed.
  (2) Determine the lightning strike zones for the aircraft.
  (3) Establish the aircraft lightning environment for each zone.
  (4) Determine the lightning transient environment associated with the systems.
  (5) Establish equipment transient design levels (ETDLs) and aircraft actual transient
  levels (ATLs).
  (6) Verify compliance to the requirements.
  (7) Take corrective measures, if needed.
   b. The steps above should be performed to
  address lightning transients induced in electrical and electronic
  system wiring and equipment, and lightning damage to aircraft external
  equipment and sensors that are connected to electrical and electronic
  systems, such as radio antennas and air data probes. Additional
  guidance on lightning protection against lightning damage for external
  equipment and sensor installations can be found in SAE ARP 5577.

Testing of individual LRUs is typically under RTCA document DO-160G - Environmental Conditions and Test Procedures for Airborne Equipment.  Section 22 covers Lightning Induced Transient Susceptibility and Section 23 covers Lightning Direct Effects.


text:
How is an on ground lightning strike test conducted?
Whenever a design company is obtaining an STC for an aircraft (Supplemental Design Certificate) for an electrical installation, one of the required tests to obtain the STC is a lightning strike test. The test is needed to show that the electronics installed can withstand a lightning strike without degrading their performance or inducing degradations into other systems.
We can't position the aircraft on ground waiting for a lightning bolt to hit like 'Doc' in 'Back to the Future', so how do design companies, or engine manufacturers, etc. simulate a lightning strike and draw conclusive results that the system with withstand actual lightning?

If you can find some local Tesla coil enthusiasts around your area that will generally be more than happy to fire off the type of voltage/current combinations at whatever you'll let them. Could even sit inside it like in the image below since it's basically acting as a Faraday cage anyway.

You create your own lightning. You can do that with an impulse generator. Here's what a smaller one looks like:

I don't know if that's what is used for the certificates but it certainly one way to test against lightning strikes (provided that you can generate a high enough voltage).

I am not positive but I think only the aircraft manufacturer uses very high voltage (enough to damage the aircraft) only on the Type Certificate.  Whereas other lightning strike tests use lower non-damaging tests, then by measuring the resulting currents one can mathematically simulate the full voltage by simply multiplying the measurements accordingly.  I only heard this from word of mouth though from an engineer at Rolls Royce.

So, Lightning Strike Test - Panthera Aircraft by Pipistrel - Episode 1 is a short video showing how Pipistrel did it. I really want to be able to push that button! :)
This page is a video and article showing how NASA does it.
Here is a Scientific American article about the why's more than the how's.

The videos both show testing just a separate bits of skin, while the electronics needs to be tested with the complete airframe.

+1 for interesting info on skin tests but as Jan mentioned I am thinking more in terms of installation onto an airframe where the lightning strikes the frames.

@esé there are facilities that can hold a small plane and fire lightning at it

Please add more than just links to your answer. Quoting the help center's How do I write a good answer?: "Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline." In this case, include a brief summary or quote describing each method.